Typical prior art compressors, such as Paget, U.S. Pat. No. 4,457,680, have but two lobes on the main rotor, which does not permit second stage ports for precompression. Also, prior art double rotor compressors usually employ similar contoured rotors, which are geared together, each serving as a compression rotor, such as Ingersoll Rand, U.S. Pat. No. 4,O68,988. Input power to one rotor is generally shared equally with the other rotor through interconnecting gears causing heavy loads and employing lubricants is required to minimize considerable wear caused therefrom. In contrast, this invention places most of the load on a single drive rotor which alone employs compression lobes. The second rotor, smaller than the compression rotor, functions as a rotary valve to eliminate sliding valves. This minimizes wear on rotor drive means, such as interconnecting gears, and reduces or eliminates the need for lubricants.
Complex contoured rotor surfaces typically found in the art also present difficulties in manufacture. In contrast, the rotors of this compressor have extended cylindrical surfaces easier to machine with the accuracy required for gas enclosure than that for complex contoured surfaces.